Illumination device including cores and clad and display device comprising the illumination device

ABSTRACT

According to one embodiment, an illumination device includes a light source, clad, and a plurality of cores. The clad includes a first edge at a light source side, a second edge opposite to the first edge, and a plurality of grooves formed by a plurality of partitions extending in parallel to each other from the first edge to the second edge. The cores are accommodated in the grooves, and each core includes an incident surface on which light from the light source is incident and an exit surface exposed from the groove to emit the light incident on the incident surface.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Priority PatentApplication JP 2014-174306 filed in the Japan Patent Office on Aug. 28,2014, the entire content of which is hereby incorporated by reference.

FIELD

Embodiments described herein relate generally to an illumination deviceand a display device.

BACKGROUND

There are known illumination devices including a light source and alight-guide having an incident surface on which light from the lightsource is incident and an exit surface from which the incident lightexits. Such illumination devices are used as a backlight of displaydevices such as a liquid crystal display device.

The light from the light source is incident on the light-guide andpropagates in the light-guide spreading radially therein, and the lightattenuates with distance from the light source. Therefore, theluminosity distribution on the exit surface of the light-guide becomesuneven such that, for example, the luminosity becomes stronger in theproximity of the light source and weaker with distance from the lightsource.

The unevenness in the luminosity distribution causes various problemsdepending on how the illumination devices are used. For example, if theillumination device is used as a backlight of a display device, theunevenness of the luminosity distribution may deteriorate the displayquality.

Each embodiment aims an illumination device which can suppressunevenness in the luminosity distribution and a display device ofexcellent display quality.

SUMMARY

This application relates generally to an illumination device and adisplay device.

In an embodiment, an illumination device comprising a light source; aclad including a first edge at a light source side, a second edgeopposite to the first edge, and a plurality of grooves formed by aplurality of partitions extending in parallel to each other from thefirst edge to the second edge; and a plurality of cores accommodated inthe grooves, each core including an incident surface on which light fromthe light source is incident and an exit surface exposed from the grooveto emit the light incident on the incident surface.

In a further embodiment, A display device comprising a first lightsource and a second light source aligned in a first direction; a cladincluding a first groove and a second groove formed by a plurality ofpartitions each extending in a second direction crossing the firstdirection; a first core accommodated in the first groove, the first coreincluding a first incident surface on which light from the first lightsource is incident and a first exit surface exposed from the firstgroove to emit the light incident from the first incident surface; asecond core accommodated in the second groove, the second core includinga second incident surface on which light from the second light source isincident and a second exit surface exposed from the second groove toemit the light incident from the second incident surface; a displaypanel including a display area with a first area opposed to the firstcore and a second area opposed to the second core; and a controllerconfigured to control luminosity of the first light source andluminosity of the second light source individually.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view which schematically shows the structure ofa display device of a first embodiment.

FIG. 2 schematically shows the structure of a liquid crystal displaypanel of the display device and an example of an equivalent circuit.

FIG. 3 is a cross-sectional view which schematically shows a structuralexample of the liquid crystal display panel.

FIG. 4 schematically shows a structural example of a backlight of thedisplay device.

FIG. 5 shows a clad and cores of a light-guide of the backlight shown inFIG. 4 in an enlarged manner.

FIG. 6 schematically shows an example of a positional relationshipbetween light-emitting diodes of the backlight and cores of alight-guide.

FIG. 7A shows a backlight of a comparative example as to the firstembodiment.

FIG. 7B shows luminosity distribution in the backlight of thecomparative example as a graph.

FIG. 8A schematically shows the backlight of the first embodiment forexplanation of an effect of the first embodiment.

FIG. 8B shows luminosity distribution of the backlight of FIG. 8A as agraph.

FIG. 9 schematically shows a part of control components of the displaydevice.

FIG. 10 shows an example of a determination method of luminosity of thelight-emitting diodes.

FIG. 11 shows a technical concept of a second embodiment.

FIG. 12 shows an example of clad shape improvement in the secondembodiment.

FIG. 13 shows a structural example of a variation of the secondembodiment.

FIG. 14 shows a structural example of a third embodiment.

FIG. 15 shows a structural example of a fourth embodiment.

FIG. 16 shows a structural example of a fifth embodiment.

FIG. 17 shows a structural example of a sixth embodiment.

FIG. 18 shows a structural example of a seventh embodiment.

FIG. 19 shows another structural example of the seventh embodiment.

FIG. 20 shows a structural example of an eighth embodiment.

FIG. 21 shows another structural example of the eighth embodiment.

DETAILED DESCRIPTION

Embodiments are described with reference to accompanying drawings. Notethat the disclosure is presented for the sake of exemplification, andany modification and variation conceived within the scope and spirit ofthe invention by a person having ordinary skill in the art are naturallyencompassed in the scope of invention of the present application.Furthermore, the width, thickness, shape, and the like of each elementare depicted schematically in the Figures as compared to actualembodiments for the sake of simpler explanation, and they are not tolimit the interpretation of the invention of the present application.Furthermore, in the description and figures of the present application,structural elements having the same or similar functions will bereferred to by the same reference numbers and detailed explanations ofthem that are considered redundant may be omitted.

In each of the following first to eighth embodiments, a display deviceis a liquid crystal display device and an illumination device is abacklight of the liquid crystal display device. For example, the liquidcrystal display device can be used in various devices such assmartphones, tablet terminals, mobilephones, notebook computers, TVs,automobiles (in-car devices), and gaming devices. Note that the displaydevice is not limited to the liquid crystal display device and may be adifferent kind of display device which includes an illumination device,such as a micro electro mechanical systems (MEMS) applied displaydevice.

First Embodiment

FIG. 1 is a perspective view which schematically shows the structure ofa liquid crystal display device LCD of a first embodiment in adisassembled manner.

A liquid crystal display device LCD includes an active matrix typeliquid crystal display panel PNL. In the example of FIG. 1, the liquidcrystal display panel PNL is formed in a rectangular shape having itsshort sides along a first direction X and long sides along a seconddirection Y which is orthogonal to the first direction X.

The liquid crystal display device LCD further includes a double-sidedtape TP, optical sheet OS, frame FR, light-guide LG, light source unitLU, reflective sheet RS1, and bezel BZ. The backlight BL is composed ofat least the light-guide LG and the light source unit LU and illuminatesthe liquid crystal display panel PNL. The backlight BL is an example ofan illumination device and may be referred to as a surface light sourcedevice.

The liquid crystal display panel PNL includes a plate-like firstsubstrate SUB1, plate-like second substrate SUB2 opposed to the firstsubstrate SUB1, and a liquid crystal layer held between the firstsubstrate SUB1 and the second substrate SUB2.

The liquid crystal display panel PNL has a display area DA whichdisplays an image within an area defined by the first substrate SUB1 andthe second substrate SUB2 opposed to each other. The liquid crystaldisplay panel PNL is of transmissive type having a transmissive displayfunction to display an image by selectively transmitting the light fromthe backlight EL. Note that the liquid crystal display panel PNL may beof transflective type having a reflective display function to display animage by selectively reflecting external light in addition to thetransmissive display function.

In the example depicted, a driver IC chip CP and a flexible printedcircuit FPC are mounted on the first substrate SUB1 as signal suppliersused to supplement of signals necessary for drive of the liquid crystaldisplay panel PNL.

The optical sheet OS is light transmissive and is disposed at the rearsurface side of the liquid crystal display panel PNL to be opposed to atleast the display area DA. The optical sheet OS includes a diffusionsheet OSA, prism sheet OSB, prism sheet OSC, and diffusion sheet OSD. Inthe example depicted, the sheets OS are each formed in a rectangle.

The frame FR is disposed between the liquid crystal display panel PNLand the bezel BZ. In the example depicted, the frame FR is formed in arectangular frame having a rectangular opening OP opposed to the displayarea DA.

The double-sided tape TP is disposed between the liquid crystal displaypanel PNL and the frame FR outside the display area DA. The double-sidedtape TP has a light-shielding property, for example, and is formed in arectangular frame-like shape to attach the liquid crystal display panelPNL and the frame FR together.

The light-guide LG is disposed between the frame FR and the bezel BZ. Inthe example depicted, the light-guide LG is formed in a plate-like shapehaving a light-emitting surface LA opposed to the liquid crystal displaypanel PNL. Note that, the light-guide LG is not necessarily formed in auniformly flat plate shape. For example, the light-guide LG may betapered in the proximity of the light source unit LU such that thelight-emitting surface LA is slanted to gradually decrease its thicknessas departing from the light source unit LU. With this structure, a spacein which the optical sheet OS is arranged can be formed on thelight-emitting surface LA.

The light source unit LU is disposed along the side surface of thelight-guide LG. The light source unit LU includes a plurality oflight-emitting diodes LD arranged in the first direction X and aflexible circuit LFPC on which the light-emitting diodes LD are mounted.The light source unit LU may include a different kind of light sourcesuch as an organic electroluminescent device instead of thelight-emitting diodes LD.

Reflective sheet RS1 is light reflective and opposed to the rear surfaceof the light-guide LG (the surface opposite to the light-emittingsurface LA). In the example depicted, reflective sheet RS1 is formed ina rectangle.

The liquid crystal display panel PNL, double-sided tape TP, opticalsheet OS, light-guide LG, and reflective sheet RS1 are layered in thisorder in a third direction Z which crosses the first direction X and thesecond direction Y orthogonally, and are accommodated by the bezel BZ.

The bezel BZ further accommodates the frame FR and the light source unitLU. For example, the optical sheet OS and the light-guide LG arepositioned inside the opening OP of the frame FR within the bezel BZ.

In the example depicted FIG. 1, the liquid crystal display panel PNL andthe frame FR are adhered by the double-sided tape TP; however, theadhesion of the liquid crystal display panel PNL and the frame FR may beperformed by a different type adhesion layer. For example, an opening OPmay be omitted from the frame FR such that the frame FR and the liquidcrystal display panel PNL are adhered to each other by a transparentadhesion layer placed to include the inner side of the display area DA.Alternately, a frame body to fix the liquid crystal display panel PNLand the backlight BL may be adopted instead of the double-sided tape TPand the adhesion layer to fix the position of the liquid crystal displaypanel PNL and the backlight BL. Note that the optical sheet OS and theframe FR are not essential and the liquid crystal display panel PNL andthe backlight BL may be adhered to each other directly.

Furthermore, in the example depicted in FIG. 1, the liquid crystaldisplay panel PNL, optical sheet OS, opening OP, and the like are eachformed in a rectangular shape; however, the shape thereof may be changedto any other polygonal shapes such as square, or circular shape, or thelike.

FIG. 2 schematically shows the structure of the liquid crystal displaypanel PNL and an example of an equivalent circuit. The liquid crystaldisplay panel PNL includes a plurality of gate lines G (G1 to Gn, n is apositive integer) extending in parallel to the first direction X, aplurality of source lines S (S1 to Sm, m is a positive integer)extending in parallel to the second direction Y, and a plurality ofsubpixels SPX arranged in an n×m matrix. Note that the subpixels SPXeach correspond to regions defined by the source lines S and the gatelines G, for example.

A subpixel SPX includes a switching element SW electrically connected toboth the gate line G and the source line S and a pixel electrode PEelectrically connected to the switching element SW. The pixel electrodePE is opposed to a common electrode CE via a liquid crystal layer LQinterposed between first substrate SUB1 and second substrate SUB2.

A pixel PX is a minimum unit to achieve color display and is composed ofa plurality of subpixels SPX. For example, a pixel PX includes subpixelsSPXR, SPXG, SPXB, and SPXW which correspond to red, green, blue, andwhite, respectively. The subpixels SPX correspond to different pixelelectrodes PE. In the example of FIG. 2, subpixels SPXR, SPXG, SPXB, andSPXW are arranged to be parallel to the first direction X. The layout ofsubpixels SPXR, SPXG, SPXB, and SPXW which are components of a pixel PXis not limited to the example of FIG. 2, and four subpixels SPXR, SPXG,SPXB, and SPXW may not be arranged in the same direction. Furthermore, apixel PX may not include a subpixel SPXW which corresponds to white butmay include a subpixel SPX of different color such as yellow.

Each gate line G is drawn outside the display area DA to be connected toa gate driver 51. Each source line S is drawn outside the display areaDA to be connected to a source driver 52. The common electrode CE iselectrically connected to a voltage supplier VS which supplies a commonvoltage through a power line PL. The gate driver 51 and the sourcedriver 52 are formed as integral circuits in the first substrate SUB1and are connected to the driver IC chip CP.

FIG. 3 is a cross-sectional view which schematically shows a structuralexample of the liquid crystal display panel PNL. In the figure, thestructure of a pixel PX including subpixels SPXR, SPXG, SPXB, and SPXWis focused.

As mentioned above, the liquid crystal display panel PNL includes thefirst substrate SUB1, second substrate SUB2 opposed to the firstsubstrate SUB1, and liquid crystal layer LQ interposed between the firstsubstrate SUB1 and the second substrate SUB2.

The first substrate SUB1 includes a first insulating substrate 10 whichis a light transmissive glass substrate or resin substrate, firstinsulating layer 11 covering the inner surface of the first insulatingsubstrate 10 (the surface at the second substrate SUB2 side), commonelectrode CE disposed on the first insulating layer 11, and secondinsulating layer 12 covering the common electrode CE. Note that aninsulating layer may be disposed on the pixel electrode PE and thecommon electrode CE may be disposed on the insulating layer.

Furthermore, the first substrate SUB1 includes pixel electrodes PER,PEG, PEB, and PEW which correspond to subpixels SPXR, SPXG, SPXB, andSPXW, respectively, and a first alignment film AL1 which covers pixelelectrodes PER, PEG, PEB, and PEW and the second insulating layer 12 andcontacts the liquid crystal layer LQ. The common electrode CE facespixel electrodes PER, PEG, PEB, and PEW with the second insulating layer12 interposed therebetween. In the example of FIG. 3, pixel electrodesPER, PEG, PEB, and PEW have a plurality of slits PSL.

The common electrode CE and pixel electrodes PER, PEG, PEB, and PEW areformed of a transparent conductive material such as indium tin oxide(ITO) or indium zinc oxide (IZO).

The second substrate SUB2 includes a second insulating substrate 20which is a light transmissive glass substrate or resin substrate, colorfilters CER, CFG, CFB, and CFW disposed on the inner surface of thesecond insulating substrate 20 (the surface at the first substrate SUB1side), and black matrix 21.

Color filter CFR is a red filter which is disposed at a red subpixelSPXR and is formed of a red colored resin material. Color filter CFG isa green filter which is disposed at a green subpixel SPXG and is formedof a green colored resin material. Color filter CFB is a blue filterwhich is disposed at a blue subpixel SPXB and is formed of a bluecolored resin material. Color filter CFW is a white filter which isdisposed at a white subpixel SPXW and is formed of a white colored resinmaterial. Note that color filter CFW may be formed of a transparentresin material or color filter CFW itself may not be disposed at aposition corresponding to a white subpixel SPXW.

In the example of FIG. 3, color filters CER, CFG, CFB, and CFW areprovided with the second substrate SUB2; however, color filters CER,CFG, CFB, and CFW may be provided with the first substrate SUB1.

The black matrix 21 defines subpixels SPXR, SPXG, SPXB, and SPXW.Boundaries of color filters CER, CFG, CFB, and CFW are positioned on theblack matrix 21. Note that, a light shielding layer may be formedinstead of such a black matrix 21 by overlaying edges of adjacent colorfilters one on another (such as CFR and CFG, CFG and CFB, and CFB andCFW).

The second substrate SUB2 further includes an overcoat layer 22 whichcovers color filters CER, CFG, CFB, and CFW and the black matrix 21, anda second alignment film AL2 which covers the overcoat layer 22 andcontacts the liquid crystal layer LQ.

A first optical element OD1 including a first polarizer plate PL1 isdisposed on the external surface of the first insulating substrate 10(the surface at the backlight BL side). Furthermore, a second opticalelement OD2 including a second polarizer plate PL2 is disposed on theexternal surface of the second substrate SUB2 (the surface opposite tothe first substrate SUB1).

The structure of FIG. 3 can be applied to, for example, a liquid crystaldisplay panel PNL of a transverse field mode which uses a transversefield substantially parallel to the main surface of the substrate inswitching of liquid crystal molecules. A structure in which pixelelectrodes PER, PEG, PEB, and PEW and the common electrode CE arearranged on the same layer or a structure in which the common electrodeCE is arranged closer to the liquid crystal layer LQ side as compared topixel electrodes PER, PEG, PEB, and PEW can be applied to the liquidcrystal display panel PNL of transverse field mode.

The mode of the liquid crystal display panel PNL is not limited totransverse field mode, but may be vertical field mode, which uses avertical field normal to the substrate surface in switching of liquidcrystal molecules, such as twisted nematic (TN) mode and verticallyaligned (VA) mode.

Next, the backlight BL will be explained.

FIG. 4 schematically shows a structural example of the backlight BL. Thelight-guide LG includes a clad 3 and a plurality of cores 4. The clad 3is formed of a first material having a first refractive index. Cores 4are formed of a second material having a second refractive index whichis greater than the first refractive index. The first and secondmaterials may be a quartz glass, multicomponent glass, and plastic, forexample.

The clad 3 is formed in a rectangular flat plate-like shape having afirst edge 3 a along the light source unit LU (and the first directionX) and a second edge 3 b opposite to the first edge 3 a. In the exampleof FIG. 4, the first edge 3 a and the second edge 3 b correspond to theshort sides of the light-guide LG.

More specifically, the clad 3 includes a first surface 30 a facing theliquid crystal display panel PNL, a second surface 30 b opposite to thefirst surface 30 a, and side surface 30 c which connects the firstsurface 30 a to the second surface 30 b.

Each core 4 extends in a slender shape along the second direction Ybetween the first edge 3 a and the second edge 3 b, and cores 4 areparallel to each other at certain intervals along the first direction X,and are disposed at the first surface 30 a side.

FIG. 5 shows the clad 3 and cores 4 in FIG. 4 in an enlarged manner.FIG. 5 schematically shows a part of the clad 3 and a part of cores 4 ina disassembled manner. The clad 3 includes a plurality of partitions 31projecting in the third direction Z on the first surface 30 a.Partitions 31 extend in parallel to each other along the seconddirection Y between the first edge 3 a and the second edge 3 b in FIG.4, and are arranged with certain intervals along the first direction X.In the example shown in FIG. 5, both the width in the first direction Xand the height in the third direction Z of each partition 31 are thesame.

Two adjacent partitions 31 form a groove 32. In other words, the clad 3includes a plurality of grooves 32 extending in the second direction Yand arranged at certain intervals along the first direction X.

A single core 4 is disposed in one groove 32. For example, across-section of core 4 parallel to X-Z plane is a uniform rectanglefrom the first edge 3 a to the second edge 3 b. Each core 4 fits in thegroove 32 and the surface of the core 4 and the inner surface of thegroove 32 are tightly adhered to each other.

As being accommodated in the groove 32, the side surface of the core 4at the first edge 3 a side which faces the light source unit LU and theupper surface in the third direction Z (the surface facing the liquidcrystal display panel PNL) are exposed. That is, the side surfaceexposed from the groove 32 is an incident surface 4 a on which lightfrom the light-emitting diodes LD is incident and the upper surfaceexposed from the groove 32 is an exit surface 4 b from which lightincident on the incident surface 4 a exits.

As in the example of FIG. 4, the side surface of the core 4 at thesecond edge 3 b side may be exposed from the groove 32 or may be coveredwith a part of the clad 3. If the side surface of the core 4 at thesecond edge 3 b side is covered by a part of the clad 3, the lightpropagating in the core 4 is reflected by the boundary between the sidesurface and the clad 3 and light loss can be decreased.

The light incident upon the incident surface 4 a enters the core 4,propagates in the core 4, and exits from the exit surface 4 b. Since therefractive index of the clad 3 is lower than that of the core 4, thelight propagating in the core 4 is totally reflected at the boundarybetween the core 4 and the clad 3.

For example, when the core 4 is accommodated in the groove 32, the top31 a of the partition 31 is flush with the exit surface 4 b of the core4. That is, the tops 31 a of the partition 31 and the exit surfaces 4 bof the cores 4 form the light-emitting surface LA of the light-guide LG.

The light-guide LG described above can be manufactured through acoinjection molding (double molding) process. In this process, a firstmold corresponding to the shape of the clad 3 is used to form the clad 3with a first material having a first refractive index. Then, the clad 3is covered with a second mold and cores 4 are formed inside the grooves32 with a second material having a second refractive index correspondingto the shape of the core 4. Through this step, the core 4 is thermallyfused with the inner wall of the groove 32. Through such a coinjectionmolding process, the light-guide LG can be manufactured accurately andeasily. Furthermore, as compared to using molding processes to form theclad 3 and the cores 4 separately, the manufacturing performance of thelight-guide LG can be improved and the manufacture cost can be reduced.

Note that the light-guide LG is not necessarily manufactured through acoinjection process and may be manufactured by any other method such asa nano-imprint process. Furthermore, the shape of the clad 3 is notlimited to a rectangular shape as in FIG. 4 and may be any polygonalshape including a square or a circular shape. Additionally, by slantingthe partitions 31 of the clad 3 and the exit surface 4 b of the cores 4,the light-guide LG may be tapered as described above.

FIG. 6 schematically shows an example of a positional relationshipbetween the light-emitting diodes LD of the light source unit LU and thecores 4 of the light-guide LG. In the example depicted, the light sourceunit LU includes six light-emitting diodes LD (LD1 to LD6).Light-emitting diodes LD1, LD2, LD3, LD4, LD5, and LD6 are arrangedalong the first direction X in this order.

In the example of FIG. 6, the light-guide LG includes thirty cores 4.The light from light-emitting diode LD1 is incident on the first tofifth cores 4 on the left. The light from light-emitting diode LD2 isincident on the sixth to tenth cores 4 from the left. The light fromlight-emitting diode LD3 is incident on the eleventh to fifteenth cores4 from the left. The light from light-emitting diode LD4 is incident onthe sixteenth to twentieth cores 4 from the left. The light fromlight-emitting diode LD5 is incident on the twenty first to twenty fifthcores 4 from the left. The light from light-emitting diode LD6 isincident on the twenty sixth to thirty cores 4 from the left.

In the description below, the five cores 4 on which the light fromlight-emitting diode LD1 is incident are referred to as group G1, thefive cores 4 on which the light from light-emitting diode LD2 isincident are referred to as group G2, the five cores 4 on which thelight from light-emitting diode LD3 is incident are referred to as groupG3, the five cores 4 on which the light from light-emitting diode LD4 isincident are referred to as group G4, the five cores 4 on which thelight from light-emitting diode LD5 is incident are referred to as groupG5, and the five cores 4 on which the light from light-emitting diodeLD6 is incident are referred to as group G6.

Furthermore, in the light-emitting surface LA, an area formed of theexit surface 4 b of the cores 4 of group G1 is referred to assub-light-emitting area SLA1, an area formed of the exit surface 4 b ofthe cores 4 of group G2 is referred to as sub-light-emitting area SLA2,an area formed of the exit surface 4 b of the cores 4 of group G3 isreferred to as sub-light-emitting area SLA3, an area formed of the exitsurface 4 b of the cores 4 of group G4 is referred to as asub-light-emitting area SLA4, an area formed of the exit surface 4 b ofthe cores 4 of group G5 is referred to as a sub-light-emitting areaSLA5, and an area formed of the exit surface 4 b of the cores 4 of groupG6 is referred to as a sub-light-emitting area SLA6.

In this structure, the luminosity of the light-emitting surface LA ofthe light-guide LG can be controlled in individual area ofsub-light-emitting areas SLA1 to SLA6 by turning on/off light-emittingdiodes LD1 to LD6 or adjusting the luminosity of light-emitting diodesLD1 to LD6 turned on. In the description below, such an area-by-areacontrol is referred to as partial drive of the backlight BL.

The partial drive of the backlight BL will be explained with referenceto FIGS. 7A and 7B and FIGS. 8A and 8B.

FIGS. 7A and 7B show a comparative example as to the present embodiment.FIG. 7A shows a backlight BL1 which includes a light-guide LG1 formeduniformly of the same material unlike the core-and-clad structure of thepresent application, and also includes light-emitting diodes LD1 to LD6arranged along an edge of light-guide LG1.

In the example of FIG. 7A, only light-emitting diode LD3 is turned onand sub-light-emitting area SLA100 emits light in a light-emittingsurface LA100 of light-guide LG1. Furthermore, the luminositydistribution in sub-light-emitting area SLA100 is represented by densityof line segments in such a manner that the luminosity increases inproportion to the density.

Since light-guide LG1 is formed uniformly, sub-light-emitting areaSLA100 spreads radially from the proximity of light-emitting diode LD3.The light incident on light-guide LG1 attenuates with distance fromlight-emitting diode LD3. Therefore, the luminosity ofsub-light-emitting area SLA100 becomes lower with distance fromlight-emitting diode LD3. Furthermore, even if the distance fromlight-emitting diode LD3 is the same, the luminosity ofsub-light-emitting area SLA100 becomes higher toward its center andbecomes lower toward its side edges. As a result, a hot spot HS havingsignificantly high luminosity as compared to the other part ofsub-light-emitting area SLA100 may possibly be generated in theproximity of light-emitting diode LD3.

FIG. 7B shows the luminosity distribution in sub-light-emitting areaSLA100 as a graph in which the horizontal axis indicates luminosity andthe vertical axis indicates a distance from light-emitting diode LD3. Ascan be understood from the graph, the luminosity reaches its peak at theposition corresponding to the hot spot HS and gradually decreases withdistance from light-emitting diode LD3.

As can be understood from the above, if each sub-light-emitting area SLAspreads radially, the sub-light-emitting areas SLA overlap by turning onlight-emitting diodes LD1 to LD6. Thus, areas for partial drive aredifficult to define in light-emitting surface LA100. Furthermore, sincethe luminosity distribution in the sub-light-emitting areas SLA isuneven, the luminosity of the image displayed in the display area DA ofthe liquid crystal display panel PNL may become uneven.

On the other hand, FIGS. 8A and 8B show an effect of the presentembodiment. FIG. 8A shows that light-emitting diode LD3 is turned on inthe backlight BL as in the case of FIG. 7A. Since light-emitting diodeLD3 is turned on, light is incident on the cores 4 of group G3 andsub-light-emitting area SLA3 emits light. The light incident on thecores 4 of group G3 propagates in the cores 4 while scarcely propagatingin the other cores 4 of the other groups. Therefore, sub-light-emittingarea SLA3 does not spread radially unlike sub-light-emitting area SLA100of the comparative example of FIG. 7A. The same applies to othersub-light-emitting areas SLA1, SLA2, and SLA4 to 6. Sincesub-light-emitting areas SLA1 to SLAG do not overlap, only a desiredarea in the light-emitting surface LA can be illuminated.

In the example of FIG. 8A, the luminosity distribution insub-light-emitting area SLA3 is represented by the density of the linefragments as in the case of FIG. 7A. Furthermore, FIG. 8B shows theluminosity distribution in sub-light-emitting area SLA3 as a graph. Insub-light-emitting area SLA3, the light incident on the cores 4 of groupG3 propagates totally reflected by the boundaries to the clad 3, andthus, the light attenuation scarcely occurs. Therefore, the luminosityin sub-light-emitting area SLA3 becomes substantially uniform regardlessof a distance from light-emitting diode LD3 and a hot spot HS does notoccur. Therefore, display quality of the image in the display area DAcan be improved.

Now, an example of control of the partial drive of the backlight unit BLwill be explained.

FIG. 9 is a block diagram which schematically shows a part of controlcomponents of the liquid crystal display device LCD. The liquid crystaldisplay device LCD includes a controller 50, gate driver 51, sourcedriver 52, and a light source driver 53 as its main control components.

The controller 50 may be composed of, for example, the drive IC chip CPas in FIG. 1, flexible printed circuit FPC, and electronic componentsmounted on the printed circuit board such as IC. The controller maycomprise other elements such as an electrical components connected tothe flexible printed circuit FPC.

The controller 50 successively receives image data per frame for thedisplay in the display area DA from a main board or the like of anelectronic device in which the liquid crystal display device LCDequipped. The image data include, for example, color data and brightnessdata used by each pixel PX of the display area DA for display. Based onthe received image data, the controller 50 supplies signals to the gatedriver 51 and the source driver 52 to drive the gate lines G (G1 to Gn)and the source lines S (S1 to Sm) connected to subpixels SPXR, SPXG,SPXB, and SPXW in the liquid crystal display panel PNL.

The gate driver 51 drives gate lines G selectively according to thesignals supplied from the controller 50. The source driver 52 drivessource lines S selectively according to the signals supplied from thecontroller 50. Subpixels in the liquid crystal display panel PNL areturned on and off individually by the drive of gate lines G and sourcelines S.

The controller 50 includes an image analysis processor 54. The imageanalysis processor 54 analyzes the image data received by the controller50 and determines the luminosity of light-emitting diodes LD of thelight source unit LU. The controller 50 supplies signals indicative ofthe luminosity determined by the image analysis processor 54 to thelight source driver 53.

The light source driver 53 turns on each light-emitting diode LD withthe luminosity indicated by the signals supplied from the controller 50by adjusting the voltage supplied to the light-emitting diode LD. Notethat, if there is a light-emitting diode LD of which luminosity isdetermined to be zero by the image analysis processor 54, the lightsource driver 53 does not turn on the light-emitting diode LD.

FIG. 10 shows an example of determination method of the luminosity oflight-emitting diodes LD by the image analysis processor 54, in whichthe backlight BL and the display area DA are depicted schematically. Inthe example depicted, six light-emitting diodes LD1 to LD6 are arrangedalong the edge of the light-guide LG as in the case of FIG. 6. That is,the light-emitting surface LA of the light-guide LG can perform partialdrive of sub-light-emitting areas SLA1 to SLA6 area by area.

In the example of FIG. 10, the display area DA includes a sub-displayarea SDA1 opposed to sub-light-emitting area SLA1, sub-display area SDA2opposed to sub-light-emitting area SLA2, sub-display area SDA3 opposedto sub-light-emitting area SLA3, sub-display area SDA4 opposed tosub-light-emitting area SLA4, sub-display area SDA5 opposed tosub-light-emitting area SLA5, and sub-display area SDA6 opposed tosub-light-emitting area SLA6.

The image analysis processor 54 calculates a total value or the averagevalue of the brightness of the pixels included in sub-display area SDA1based on the image data and determines the luminosity of light-emittingdiode LD1 based on the total value or the average value. Here, the imageanalysis processor 54 uses a predetermined operation formula or tableand gives a higher value to the luminosity as the total value or theaverage value of the brightness increases. Similarly, the luminosity ofeach of light-emitting diodes LD2 to LD6 can be determined based on atotal value or the average value of the brightness of pixels PX includedin respective sub-display areas SDA2 to SDA6.

In the example of FIG. 10, an image I is displayed in the display areaDA. The image I includes a high-brightness part HB emerging oversub-display areas SDA2 and SDA3. The part other than the high-brightnesspart HB has substantially zero brightness (black). When using image dataof the image I, the image analysis processor 54 gives first luminositywhich is high to light-emitting diodes LD2 and LD3 corresponding tosub-display areas SDA2 and SDA3 and gives second luminosity which islower than the first luminosity to light-emitting diodes LD1, and LD4 toLD6 corresponding to sub-display areas SDA1, and SDA4 to SDA6. Thesecond luminosity may be zero and if it is, light-emitting diodes LD1and LD4 to LD6 are not turned on.

As can be understood from the above, the luminosity of light-emittingdiodes LD1 to LD6 is determined based on the brightness of the imagedisplayed in the display area DA, and as a result, high quality imagedisplay having a high contrast ratio can be achieved. For example, theimage I in FIG. 10 is displayed by light-emitting diodes LD2 and LD3turned on with the first luminosity and light-emitting diodes LD1 andLD4 to LD6 turned on (or turned off) with the second luminosity which isless than the first luminosity, and therefore, a contrast ratio betweenthe image displayed in sub-display areas SDA2 and SDA3 and the imagedisplayed in sub-display areas SDA1 and SDA4 to SDA6 can be increased.

Furthermore, in a general liquid crystal display device, displayingblack by switching liquid crystal molecules of a liquid crystal displaypanel while turning on a backlight is difficult since light from thebacklight cannot be completely shielded by the liquid crystal displaypanel. Certain amount of light leaks from the display area DA and pureblack cannot be displayed. In contrast, with the structure of thepresent embodiment, when a sub-display area SDA display an image ofblack entirely or substantially entirely, a light-emitting diode LDcorresponding to the sub-display area SDA is turned off or turned onwith very low luminosity, and black can be displayed with almost nolight leaking.

Furthermore, light-emitting diodes LD which are not necessarily turnedon with high luminosity are turned on with lower luminosity or turnedoff, and thus, the power consumed in the backlight BL can be suppressed.

Furthermore, as in FIGS. 2 and 3, a pixel PX may include a whitesubpixel SPXW. If the white subpixel SPXW is used appropriately in thecolor display of the pixel PX, the brightness of the entirety of thedisplay area DA can be increased. Thus, the luminosity of thelight-emitting diodes LD can be decreased as a whole and the powerconsumed in the backlight BL can be suppressed more.

Examples of the display device achieved from the disclosure of thepresent embodiment are noted below. The reference numerals in bracketsmay correspond to those applied to structural elements explained in thepresent embodiment. Examples below do not limit the scope of theinvention and various display devices and illumination devices can beachieved from the disclosure of the present embodiment.

Note 1

An illumination device comprising:

a light source (LD);

a clad (3) including a first edge (3 a) at the light source side, asecond edge (3 b) opposite to the first edge, and a plurality of grooves(32) formed by a plurality of partitions (31) extending in parallel toeach other from the first edge to the second edge; and

a plurality of cores (4) accommodated in the grooves, each coreincluding an incident surface (4 a) on which light from the light sourceis incident and an exit surface (4 b) exposed from the groove to emitthe light incident on the incident surface.

Note 2

A display device comprising:

a first light source (LD1) and a second light source (LD2) aligned in afirst direction (X);

a clad (3) including a first groove (32) and a second groove (32) formedby a plurality of partitions (31) each extending in a second direction(Y) crossing the first direction;

a first core (4) accommodated in the first groove, the first coreincluding a first incident surface (4 a) on which light from the firstlight source is incident and a first exit surface (4 b) exposed from thefirst groove to emit the light incident from the first incident surface;

a second core (4) accommodated in the second groove, the second coreincluding a second incident surface (4 a) on which light from the secondlight source is incident and a second exit surface (4 a) exposed fromthe second groove to emit the light incident from the second incidentsurface;

a display panel (PNL) including a display area (DA) with a first area(SDA1) opposed to the first core and a second area (SDA2) opposed to thesecond core; and

a controller (50) configured to control luminosity of the first lightsource and luminosity of the second light source individually.

Second Embodiment

Now, the second embodiment will be explained. Unless otherwisespecified, the structure, advantage, and the like are the same as thoseof the first embodiment.

As explained with reference to FIG. 6, if there are groups G (G1 to G6)of a plurality of cores 4 corresponding to a plurality light-emittingdiodes LD (LD1 to LD6), boundary stripes may appear at boundaries ofgroups G with lower luminosity as compared to the other parts. That is,since the light from the light-emitting diodes LD incident on the cores4 becomes weaker with distance of the cores 4 from the light-emittingdiodes LD in the first direction X, the luminosity of the light from theexit surface 4 b of the core 4 positioned at the boundary of twoadjacent light-emitting diodes LD is lower as compared to that of theother cores 4. Thus, the luminosity possibly becomes uneven along thefirst direction X when the light-emitting surface LA is viewed as awhole. Such unevenness in luminosity may cause deterioration of thedisplay quality of the liquid crystal display device LCD.

FIG. 11 shows an example of a method of preventing boundary stripes.FIG. 11 schematically shows three light-emitting diodes LD1, LD2, andLD3 and eleven cores 4 at its bottom. Light from light-emitting diodeLD1 is incident on the first and fifth cores 4 on the left. Light fromlight-emitting diode LD2 is incident on the fourth to eighth cores 4from the left. Light from light-emitting diode LD3 is incident on theseventh to eleventh cores 4 from the left.

As above, in the example of FIG. 11, light from adjacent light-emittingdiodes LD (LD1 and LD2, LD2 and LD3) is incident on two cores 4 betweenthese adjacent light-emitting diodes LD (LD1 and LD2, LD2 and LD3).

A curve C1 in FIG. 11 shows an example of luminosity distribution oflight from light-emitting diode LD1 which is turned on with optionalluminosity, and the luminosity distribution is on the light-emittingsurface LA along the first direction X at a position distant fromlight-emitting diode LD1 by an optional distance in the second directionY. A curve C2 shows an example of luminosity distribution of light fromlight-emitting diode LD2 which is turned on with the same optionalluminosity, and the luminosity distribution is on the light-emittingsurface LA along the first direction X at a position distant fromlight-emitting diode LD1 by the same optional distance in the seconddirection Y. A curve C3 shows an example of luminosity distribution oflight from light-emitting diode LD3 which is turned on with the sameoptional luminosity, and the luminosity distribution is on thelight-emitting surface LA along the first direction X at a positiondistant from light-emitting diode LD1 by the same optional distance inthe second direction Y.

The luminosity distribution of each of curves C1 to C3 indicates thatthe luminosity is high at the direct front of light-emitting diode LDand becomes lower with distance from light-emitting diodes LD in thefirst direction X. A straight line L on curves C1 to C3 represents thetotal luminosity which is an addition of the luminosity of curves C1 toC3 in each position in the first direction X. As is evident from thetotal luminosity represented by the straight line L, unevenness inluminosity in the first direction X does not occur in the example ofFIG. 11. Therefore, a boundary stripe as explained above does not occur.

As above, light emitted from adjacent light-emitting diodes LD isincident on the core 4 therebetween to prevent the unevenness inluminosity in the first direction X.

The total luminosity may not necessarily be a straight line. Even if theline is crooked to a certain extent, the display quality of the liquidcrystal display device LCD can still be improved.

The number of cores 4 on which light from both adjacent light-emittingdiodes LD is incident is not limited to two. It may be one or may bethree or more.

To achieve the luminosity distribution without unevenness as representedby the straight line L shown in FIG. 11, the shape of clad 3 and cores4, the material of clad 3 and cores 4, the distance betweenlight-emitting diodes LD and the clad 3, and the distance betweenlight-emitting diodes LD and cores 4 may be improved suitably inaddition to providing cores 4 on which light from adjacentlight-emitting diodes LD.

An example of improvement of the shape of clad 3 will be explained withreference to FIG. 12. FIG. 12 schematically shows three light-emittingdiodes LD1, LD2, and LD3 and a plurality of cores 4 on which light fromlight-emitting diodes LD1 to LD3 is incident. Unlike the example of FIG.11, light from each of light-emitting diodes LD1 to LD3 is incident onseven cores 4. The number of cores 4 on which light from adjacentlight-emitting diodes LD (LD1 and LD2, LD2 and LD3) is two.

In the example of FIG. 12, partitions 31 between cores 4 on which lightfrom one light-emitting diode LD is incident are changed in thicknesssuch that the partition becomes thinner with distance from the directfront of the light-emitting diode LD. Considering six partitions 31between seven cores 4 on which light from light-emitting diode LD2, forexample, the width of each of two partitions 31 at their center is W1,the width of each of next two partitions 31 is W2 which is less than W1,and the width of each of next two partitions 31 is W3 which is less thanW2 (W1>W2>W3). In the example of FIG. 12, cores 4 have the same width.

In the example of FIG. 12, partitions 31 include first partitionspositioned between adjacent light-emitting diodes LD and secondpartitions positioned in front of light-emitting diodes LD. Firstpartition has a first width which is narrower than a second width ofsecond partition. The first partitions are partitions 31 positioned in aslanting direction of light-emitting diodes LD (positioned in adirection crossing both the first direction X and the second directionY). Therefore, a first distance between the first partitions andlight-emitting diodes LD is longer than a second distance between thesecond partitions and light-emitting diodes LD. From a differentstandpoint, the first partitions are interpreted as partitions 31positioned between the second partitions positioned in front oflight-emitting diodes LD.

As above, since a partition 31 becomes narrower as reaching a boundaryof adjacent light-emitting diodes LD, an area occupied by partition 31decreases in the proximity of the boundary. The partition 31 does notemit light or make any contribution to the improvement of theluminosity, and such a reduced area of the partition 31 can increase theluminosity in the proximity of the boundary. That is, unevenness of theluminosity in the first direction X can be suppressed by changing thewidth of the partition 31.

Note that the width of the partition 31 is changed in the example above;however, cores 4 may be changed in thickness such that the core 4becomes wider as reaching a boundary of adjacent light-emitting diodesLD to adjust the luminosity of the light-emitting surface LA.Considering, for example, light from one light-emitting diode LD isincident on seven cores 4 and the number of cores 4 on which light fromadjacent light-emitting diodes LD is two, the width of each of two cores4 at their center is W3, the width of each of next two cores 4 is W2,and the width of each of next two cores 4 is W1 (W1>W2>W3).

Furthermore, both the width of partition 31 and the width of cores 4 canbe adjusted.

In the second embodiment described above, a core 4 on which light fromtwo adjacent light-emitting diodes LD is used to suppress boundarystripes. However, this is not the only method to suppress boundarystripes. For example, boundary stripes can be suppressed by providingpinholes with the partition 31 to guide light alternately between a core4 at one side and a core 4 at the other side of the partition 31.

FIG. 13 shows an example of the structure of the above variation, andFIG. 13 schematically shows a cross-section of the clad 3 and thelight-emitting diode LD taken along the Y-Z plane. In the example ofFIG. 13, the partition 31 of the clad 3 has a plurality of pinholes 33passing through a groove 32 at the one side to a groove 32 at the otherside. Note that the pinhole 33 may not necessarily be a circular holeand may be a notch made on the partition 31 from the top 31 a side.

Light which propagates the core 4 at one side of the partition 31partially leaks from the pinholes 33 and is incident on the core 4 atthe other side. That is, each light propagates these cores 4 is mixedwith one another through pinholes 33 and the luminosity of the exitsurface 4 b of these cores 4 becomes uniform. As a result, unevenness ofthe luminosity of the light-emitting surface LA in the first direction Xcan be suppressed and generation of the boundary stripes can beprevented.

Pinholes 33 may not necessarily be provided with the entire partitions31. For example, partitions 111 positioned in front of light-emittingdiodes LD may not include pinholes 33 and only one or more partitions 31positioned between adjacent light-emitting diodes LD may includepinholes 33. Alternately, for example, the number of pinholes 33 may bechanged partition by partition such that the number of pinholes 33 inthe partitions 31 gradually reduces as becoming close to the front oflight-emitting diodes LD.

The light which is incident on the core 4 from the first edge 3 a sideattenuates as propagating to the second edge 3 b side. Considering thispoint, the density of pinholes 33 may be gradually decreased toward thesecond edge 3 b side from the first edge 3 a side in the partition 31 asshown in FIG. 13. Note that, instead of changing the density, the sizeof pinhole 33 (area of opening, diameter, or the like) may be graduallyreduced toward the second edge 3 b side from the first edge 3 a side.

Furthermore, if pinholes 33 are arranged in pattern such that pinholes33 are arranged in the same positions in each partition 31 in the seconddirection Y, light leaking through the pinholes 33 may possibly berecognized as stripes. Considering this point, pinholes 33 in eachpartition 31 may be arranged randomly.

Third Embodiment

The third embodiment will be explained. Unless otherwise specified, thestructure, advantage, and the like are the same as those of the firstembodiment.

FIG. 14 shows a structural example of the third embodiment, and FIG. 14shows the light-guide LG, reflective sheet RS1 of FIG. 1, and otherreflective sheets RS2, RS3, and RS4. Reflective sheet RS1 is providedwith the rear surface of the light-guide LG (the second surface 30 b ofthe clad 3). Reflective sheets RS2 and RS3 are provided with two sidesurfaces along the second direction Y of the side surfaces 30 c of theclad 3. Reflective sheet RS4 is provided with the side surface at thesecond edge 3 b side of the side surfaces 30 c of the clad 3. Reflectivesheets RS1 to RS4 are adhered to respective surfaces of the clad 3 via,for example, adhesive layers.

Light from light-emitting diodes LD to be incident on the cores 4scarcely leaks to the clad 3 from the cores 4 because of a reflectiveindex different between the clad 3 and the cores 4. However, lightoutgoing from the exit surface 4 b of the cores 4 is reflected by theoptical sheet OS and the liquid crystal display panel PNL, and returnsto the light-guide LG. Such light may possibly pass the clad 3 and thecores 4 and leak from the second surface 30 b of the clad 3 (the rearsurface of the light-guide LG) and from the side surface 30 c (the sidesurface of the light-guide LG).

With reflective sheets RS1 to RS4, the light leaking from the rearsurface of the light-guide LG is reflected to the clad 3 by reflectivesheet RS1, and the light leaking from the side surfaces of thelight-guide LG is reflected to the clad 3 by reflective sheets RS2 toRS4. The reflected light is used effectively to increase the efficiencyof the backlight BL.

Note that reflective sheets RS1 to RS4 may not necessarily be providedwith the light-guide LG as a whole, and only one, two, or three of thesheets may be provided. Furthermore, reflective sheet RS1 may partiallycover the second surface 30 b and reflective sheets RS2 to RS4 maypartially cover their corresponding side surfaces 30 c.

Fourth Embodiment

The fourth embodiment will be explained. Unless otherwise specified, thestructure, advantage, and the like are the same as those of the firstembodiment.

The present embodiment is related to an example of a method of emittinglight incident on cores 4 from an exit surface 4 b. FIG. 15 shows astructural example of the fourth embodiment and schematically shows across-section of a clad 3, core 4, and light-emitting diode LD takenalong the Y-Z plane.

The core 4 in the example of FIG. 15 has a plurality of projections PTon the exit surface 4 b. The projections PT are a half-sphere dotpattern formed on the exit surface 4 b, for example. As another example,the projections PT may be a prism pattern formed on the exit surface 4b.

Projects PT as a dot pattern or a prism pattern are formed along with orafter the formation of the cores 4 on the exit surface 4 b by treatingthe exit surface 4 b, or may be formed separately from the cores 4 onthe exit surface 4 b. The projections PT are provided with the bottomsurface of the core 4 contacting the clad 3 (the surface opposite to theexit surface 4 b).

The projections PT are effective to improve the efficiency of the lightemission by which light propagating inside the core 4 is emittedoutside.

If the efficiency of the light emission of the exit surface 4 bdecreases with distance from the incident surface 4 a, the luminosity ofthe exit surface 4 b may be made uniform by gradually increasing thedensity of the projections PT toward the opposite side to the incidentsurface 4 a as shown in FIG. 15.

Note that the core 4 may have recesses on the exit surface 4 b insteadof the projections PT. For example, the recess may be formed in ahalf-spherical shape or a polygonal shape. The recesses may be providedwith the bottom surface of the core 4 contacting the clad 3. In asimilar manner to the formation of the projections PT, the density ofthe recesses may be changed.

If a reflective sheet RS4 is provided with the side surface of the clad3 at the second end 3 b side as in the third embodiment, the luminosityof the exit surface 4 b may become high at the second end 3 b side bythe reflected light from the reflective sheet RS4. Considering thispoint, the density of projections PT or recesses may be increased withdistance from the second end 3 b. Or, the density of projections PT orrecesses may be increased with distance from the incident surface 4 a toa certain point and decreased with distance from the point to the secondend 3 b. For example, the point may be set to be closer to the secondend 3 b side with reference to the center of the core 4 in the seconddirection Y.

Fifth Embodiment

The fifth embodiment will be explained. Unless otherwise specified, thestructure, advantage, and the like are the same as those of the firstembodiment.

The present embodiment is related to an example of a method of emittinglight incident on cores 4 from the exit surface 4 b. FIG. 16 shows astructural example of the fifth embodiment and schematically shows across-section of a clad 3 and cores 4 taken along the X-Y plane.

The cores 4 of the example of FIG. 16 include a large number ofdiffusion structures ST inside thereof. The diffusion structure ST isformed of a material different from the base material of the core 4, forexample. As another example, the diffusion structure ST may be a gap(bubble).

The diffusion structures ST are effective to improve the efficiency ofthe light emission by which light propagating inside the core 4 isemitted outside.

If the efficiency of the light emission of the exit surface 4 bdecreases with distance from the incident surface 4 a, the luminosity ofthe exit surface 4 b may be made uniform by gradually increasing thedensity of the diffusion structures ST toward the opposite side to theincident surface 4 a as shown in FIG. 16.

If a reflective sheet RS4 is provided, the density of the diffusionstructures ST may be increased with distance from the second end 3 b asin the fourth embodiment. Or, the density of the diffusion structures STmay be increased with distance from the incident surface 4 a to acertain point and decreased with distance from the point to the secondend 3 b.

Sixth Embodiment

The sixth embodiment will be explained. Unless otherwise specified, thestructure, advantage, and the like are the same as those of the firstembodiment.

The present embodiment is related to an example of a method of emittinglight incident on cores 4 from an exit surface 4 b. FIG. 17 shows astructural example of the fourth embodiment and schematically shows across-section of a clad 3, core 4, and light-emitting diode LD takenalong the Y-Z plane.

In the example of FIG. 17, the core 4 is formed in a wedge shape. Thatis, a thickness T1 of the core 4 in the third direction Z (normal to theexit surface 4 b) decreases with distance from the incident surface 4 ain the second direction Y. In contrast, a thickness T2 of the clad 3 inthe third direction Z increases with distance from the first edge 3 a inthe second direction Y.

With this structure, the light incident on the cores 4 from thelight-emitting diodes LD is reflected to the exit surface 4 b at theboundary between the rear surface 4 c of the cores 4 (the oppositesurface to the exit surface 4 b) and the clad 3. Thus, the light cansuitably be emitted from the exit surface 4 b.

Note that FIG. 17 shows a structural example in which both the clad 3and the cores 4 change their thicknesses with distance from the incidentsurface 4 a in the second direction Y; however, only the thickness ofthe cores 4 may be changed while the thickness of the clad 3 is keptconstant.

If a reflective sheet RS4 is provided, the thickness T1 of the core 4may be decreased with distance from the second end 3 b for facilitatedejection of the reflected light from the exit surface 4 a. Or, thethickness T1 of the core 4 may be decreased with distance from theincident surface 4 a to a certain point, and increased with distancefrom the point to the second end 3 b.

Seventh Embodiment

The seventh embodiment will be explained. Unless otherwise specified,the structure, advantage, and the like are the same as those of thefirst embodiment.

Light from light-emitting diodes LD and incident on the light-guide LGis mainly emitted from the exit surfaces 4 b of core 4. Thus, stripes oflow luminosity may possibly be generated at tops 31 a of partitions 31of a clad 3 in the light-emitting surface LA. The present embodiment isrelated to a method of preventing or lessening such stripes.

FIGS. 18 and 19 show a structural example of the seventh embodiment andschematically show a cross-section of the clad 3 and cores 4 taken alongthe X-Z plane, respectively. In the examples of these figures, each top31 a of the partition 31 of the clad 3 is narrowed toward its tip andeach core 4 is widened in the first direction X to correspond to theshape of the top 31 a.

In the example of FIG. 18, the top 31 a is rounded in an arc-like shape,and the core 4 is filled to the tip of the top 31 a rounded in anarc-like shape. In the example of FIG. 19, the top 31 a is taperedtoward the tip of the top 31 a and the core 4 is filled to the tip ofthe tapered top 31 a.

With these structures, the exit surfaces 4 b are spread over thepartitions 31. Thus, the stripes caused by the partitions 31 can beprevented or lessened.

Note that, in the examples of FIGS. 18 and 19, adjacent cores 4 aredivided by the partitions 31. However, adjacent cores 4 may be connectedto each other over the tips of the partitions 31.

Eighth Embodiment

The eighth embodiment will be explained. Unless otherwise specified, thestructure, advantage, and the like are the same as those of the firstembodiment.

The present embodiment is related to a method of efficiently guidinglight from light-emitting diodes LD to incident surfaces 4 a of cores 4.

FIG. 20 shows a structural example of the eighth embodiment andschematically shows a part of a backlight BL. The backlight BL includesa plurality of lenses 90 arranged between light-emitting diodes LD and alight-guide LG. The lens 90 is a concave lens including an arc-likeshape recess 91.

In the example of FIG. 20, the lens 90 faces five incident surfaces 4 aof five consecutive cores 4. A light-emitting diode LD is arranged inthe recess 91 of the lens 90. The lens 90 radiates the light from thelight-emitting diode LD and emits the radiated light from the surfaceopposite to the recess 91. The light emitted from the lens 90 isincident on the incident surfaces 4 a of the cores 4 facing the lens 90.Using the lens 90, the light from the light-emitting diodes LD caneffectively be guided to the incident surfaces 4 a of the cores 4.

Note that, if the light-emitting diodes LD are arranged to be close tothe lenses 90, heat from the light-emitting diodes LD easily reaches thelenses 90. For example, if the lens 90 is formed of a material ofexcellent heat resistivity and heat insulation, deformation of the lens90 caused by the heat from the light-emitting diode LD can be suppressedand the heat transmittance from the light-emitting diodes LD to thelight-guide LG can be prevented.

FIG. 21 schematically shows another example of the lens 90. In theexample depicted, the lens 90 is formed continuously between thelight-emitting diodes LD of the light source unit LU and the light-guideLG, and the lens 90 includes a plurality of recesses 91 corresponding tothe arrangement positions of the light-emitting diodes LD. The lens 90with such a structure can guide the light from the light-emitting diodesLD to the incident surfaces 4 a of the cores 4.

Here, an interface may be created between every two adjacent lenses 90in the example of FIG. 20, but an interface is not created in theexample of FIG. 21. Therefore, the lens 90 of the example of FIG. 21 caneasily be applied to a case where light from adjacent light-emittingdiodes LD is guided to the cores 4 therebetween as in the secondembodiment.

The structures of the embodiments described above can be combinedarbitrarily or modified in various ways. For example, in each of theembodiments described above, a backlight equipped in a liquid crystaldisplay device is exemplified as an illumination device. However, thestructure of the backlight disclosed in each of the embodiment describedabove can be applied to a front light used in a reflective type displaydevice.

Furthermore, additional advantages obtained from the first to eighthembodiments are, as long as they are obvious from the disclosure of thepresent application or easily conceivable from a person having ordinaryskill in the art, naturally encompassed by the scope of the presentapplication.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. An illumination devicecomprising: a plurality of light sources; a clad including a first edgeat a light source side, a second edge opposite to the first edge, and aplurality of grooves formed by a plurality of partitions, wherein thegrooves extend in parallel to each other from the first edge to thesecond edge; and a plurality of cores corresponding to each of the lightsources and accommodated in the grooves, each core including an incidentsurface on which light from the light source is incident and an exitsurface exposed from the groove to emit the light incident on theincident surface, wherein the light sources are arranged along the firstedge, wherein the partitions include a first partition positionedbetween the light sources and a second partition positioned in front ofone of the light sources, and wherein a first width of the firstpartition is less than a second width of the second partition.
 2. Theillumination device of claim 1, wherein the clad is formed of a firstmaterial having a first refractive index, and the core is formed of asecond material having a second refractive index which is greater thanthe first refractive index.
 3. The illumination device of claim 1,wherein the core includes a plurality of projections or recesses formedon the exit surface, the projections or the recesses configured to emitlight propagating in the core.
 4. The illumination device of claim 3,wherein density of the projections or the recesses increases withdistance from the incident surface.
 5. The illumination device of claim1, wherein the core includes a plurality of diffusion structures insidethereof, the diffusion structures configured to diffuse lightpropagating in the core.
 6. The illumination device of claim 5, whereindensity of the diffusion structures increases with distance from theincident surface.
 7. The illumination device of claim 1, wherein athickness of the core normal to the exit surface decreases with distancefrom the incident surface.
 8. The illumination device of claim 1,wherein the core is widened in the proximity of a top of the partitiontoward a tip thereof.
 9. The illumination device of claim 1, furthercomprising a lens disposed between the light source and the incidentsurface of each core, the lens configured to radiate light from thelight source to be incident on the incident surface, wherein light fromthe lens is incident on the plurality of the cores.
 10. The illuminationdevice of claim 9, wherein the lens is wider than each of the cores in adirection in which the cores are arranged.
 11. The illumination deviceof claim 1, wherein the clad includes a first surface on which thepartitions are formed, a second surface opposite to the first surface,and side surfaces between the first and second surfaces, and theillumination device further comprises a reflective sheet provided on atleast a part of the second surface and the side surfaces, the reflectivesheet configured to reflect light leaking from the clad back to theclad.
 12. The illumination device of claim 1, further comprising: acontroller, wherein the light source includes a first light source and asecond light source aligned in a first direction, wherein the groovesinclude first grooves and second grooves, wherein the cores includefirst cores accommodated in the first grooves, each first core includinga first incident surface on which light from the first light source isincident and a first exit surface exposed from a corresponding one ofthe first grooves to emit the light incident from the first incidentsurface, wherein the cores include second cores accommodated in thesecond grooves, each second core including a second incident surface onwhich light from the second light source is incident and a second exitsurface exposed from a corresponding one of the second grooves to emitthe light incident from the second incident surface, and wherein thecontroller is configured to control luminosity of the first light sourceand luminosity of the second light source individually.
 13. Anillumination device comprising: a light source; a clad including a firstedge at a light source side, a second edge opposite to the first edge,and a plurality of grooves formed by a plurality of partitions, whereinthe grooves extend in parallel to each other from the first edge to thesecond edge; and a plurality of cores accommodated in the grooves, eachcore including an incident surface on which light from the light sourceis incident and an exit surface exposed from the groove to emit thelight incident on the incident surface, wherein the clad is formed of afirst material having a first refractive index, the core is formed of asecond material having a second refractive index which is greater thanthe first refractive index, and a top of the partition is shaped to benarrower toward a tip thereof.
 14. The illumination device of claim 13,wherein the top is formed in an arc-shape or in a tapered-shape narrowedtoward the tip.
 15. The illumination device of claim 13, furthercomprising: a controller, wherein the light source includes a firstlight source and a second light source aligned in a first direction,wherein the grooves include first grooves and second grooves, whereinthe cores include first cores accommodated in the first grooves, eachfirst core including a first incident surface on which light from thefirst light source is incident and a first exit surface exposed from acorresponding one of the first grooves to emit the light incident fromthe first incident surface, wherein the cores include second coresaccommodated in the second grooves, each second core including a secondincident surface on which light from the second light source is incidentand a second exit surface exposed from a corresponding one of the secondgrooves to emit the light incident from the second incident surface, andwherein the controller is configured to control luminosity of the firstlight source and luminosity of the second light source individually. 16.An illumination device, comprising: a light source; a clad including afirst edge at a light source side, a second edge opposite to the firstedge, and a plurality of grooves formed by a plurality of partitions,wherein the grooves extend in parallel to each other from the first edgeto the second edge; and a plurality of cores accommodated in thegrooves, each core including an incident surface on which light from thelight source is incident and an exit surface exposed from acorresponding one of the grooves to emit the light incident on theincident surface, wherein at least one of the partitions includes aplurality of holes pierced through two grooves adjacent each other. 17.The illumination device of claim 16, further comprising: a controller,wherein the light source includes a first light source and a secondlight source aligned in a first direction, wherein the grooves includingfirst grooves and second grooves, wherein the cores include first coresaccommodated in the first grooves, each first core including a firstincident surface on which light from the first light source is incidentand a first exit surface exposed from a corresponding one of the firstgrooves to emit the light incident from the first incident surface,wherein the cores include second cores accommodated in the secondgrooves, each second core including a second incident surface on whichlight from the second light source is incident and a second exit surfaceexposed from a corresponding one of the second grooves to emit the lightincident from the second incident surface, and wherein the controller isconfigured to control luminosity of the first light source andluminosity of the second light source individually.
 18. The displaydevice of claim 17, wherein the controller is configured to control theluminosity of the first light source according to brightness of a firstimage displayed in a first area of a display panel opposed to the firstcores and the luminosity of the second light source according tobrightness of a second image displayed in a second area of the displaypanel opposed to the second cores.